Process for preparing aromatic isocyanates

ABSTRACT

The process for preparing an organic isocyanate by reacting an organic nitro compound with carbon monoxide in the presence of a catalytic system comprised of a mixture of at least one compound selected from the group consisting of palladium halides, rhodium halides, palladium oxides, and rhodium oxides, with at least one oxide of an element selected from the group consisting of vanadium, molybdenum, tungsten, niobium, chromium, and tantalum.

United States Patent; 1191 Schnabel et al.

PROCESS FOR PREPARING AROMATIC ISOCYANATES Inventors: Wilhelm J.Schnabel, Branford; Ehrenfried l-l. Kober, Hamden; Theodore C. Kraus,Cheshire, all of Conn.

Olin Mathieson Chemical Corporation Assignee:

Filed: Feb. 28, 1967 Appl. No.: 619,158

us. 01 ..260/453 PC, 252/441, 252/470,

252/472 Int. Cl ..c07 119/04 Field of Search ..,......2 0/453 A, 453 PCReferences Cited FOREIGN PATENTS OR APPLlCATlONS 5/1966 Belgium OTHER PUBLlCATlONS Olah; Friedel-Crafts and Related Reactions, Volume l, Pages310-312; 329-330 relied upon, 1963, lnterscience Publishers, New York.

Primary Exa minerLewis Gotts Assistant ExaminerDolph H. TorrenceAttorney-Gordon D. By'rkit, Donald F. Clements,-

Walter D. Hunter, Thomas P. O Day, Ellen P. Trevors, Arthur N. Krein,Richard S. Strickler and George J. Koeser [57] ABSTRACT 12 Claims, NoDrawings 7 3,714,216 1. 51 Jan. 30, 1973- PROCESS FOR PREPARING AROMATICISOCYANATES This invention relates to the preparation of organicisocyanates from organic nitro compounds.

Organic isocyanates are used extensively in the preparation of urethanefoams, coatings, and fibers, as well as in the preparation ofinsecticides, pesticides and the like. Commercial processes forpreparing organic isocyanates utilize the catalytic hydrogenation of anorganic nitro compound to form the corresponding amine, followed byreaction of the amine with phosgene to form the correspondingisocyanate. These processes are complex and expensive,'and the need fora simplified, less expensive process is apparent.

In order to provide a simplified technique, it has been proposed toreact an organic nitro compound with carbon monoxide in the presence ofa catalyst. For example, British Pat. No. 1,025,436 discloses a processfor preparing isocyanates from the corresponding nitro compounds byreacting an organic nitro compound with carbon monoxide in the'presenceof a noble metalbased catalyst. This process is not used commerciallybecause no more than trace amounts of organic isocyanates are formedwhen an organic nitro compound such as dinitrotoluene is reacted withcarbon monoxide using a noble metal-based catalyst, such as rhodiumtrichloride, palladium dichloride, iridium trichloride, osmiumtrichloride and the like.

Other proposed simplified techniques utilize other catalyst systems. Forexample, Belgium Pat. No. 672,405, entitled Process For The PreparationOf Organic isocyanates, describes the use of a catalyst system of anoble metal and/or a Lewis acid in the reaction between an organic nitrocompound with carbon monoxide.

Unfortunately, the yield of organic isocyanate afforded by thesesimplified techniques has not been significant enough to justify theiruse on a commercial scale. v

It is a primary object of this invention to provide an improved processfor the preparation of organic isocyanates.

Another object of the invention is to provide a novel catalyst systemuseful in the direct conversion of organic nitro compounds to thecorresponding organic isocyanates.

Still a further object is to provide 'an improved process for preparingphenyl isocyanate.

It is another object of the invention to provide an improved process forpreparing toluene diisocyanates.

Another object of the invention is to provide an improved process forpreparing isocyanato-nitrotoluenes.

These and other objects of the invention'will be apparent from thefollowing detailed description thereof.

It has now been discovered that the above-mentioned objects areaccomplished when an organic nitro compound is reacted with carbonmonoxide at an elevated pressure and elevated temperature inv thepresence of a catalyst system comprised of a mixture of at least onecompound selected from the group consisting of palladium halides,rhodium halides, palladium oxides and rhodium oxides, with at least oneoxide of an element selected from the group consisting of vanadium,molybdenum, tungsten, niobium, chromium and tantalum.

nitro compounds of the type described herein. Typical examples ofsuitable organic nitro compounds which can be reacted to formisocyanates include the following:

l. Aromatic Nit'ro Compounds a. Nitrobenzene b. Nitronaphthalenes c.Nitroanthracenes d. Nitrobiphenyls e. Bis(nitrophenyl)methanes f.Bis(nitrophenyl)ethers v g. Bis(nitrophenyhthioether h.l3is(nitrophenyl)sulfones i. Nitrodiphenoxy alkanes j.Nitrophenothiazines ll. Nitrocycloalkanes a. Nitrocyclobutane b.Nitrocyclopentane c. Nitrocyclohexane d. Dinitrocyclohexanes e.Bis(nitrocyclohexyhmethanes lll. Nitroalkanes a. Nitromethane b.Nitroethane c. Nitropropane d. l litrobutanes e. Nitrohexanes f.Nitrooctanes g. Nitrooctadecanes h. Dinitroethane i. Dinitropropanes j.Dinitrobutanes k. Dinitrohexanes l. Dinitrodecanes rn. Phenylnitromethane n. Bromophenyl nitrometha'nes o. Nitrophenyl nitromethanesp. Methoxy phenyl nitromethanes q. Bis-(nitromethyl)cyclohexanes r.Bis-(nitromethyl)benzenes All of the aforementioned compounds may besubstituedwith one or more additional substituents such as nitro,nitro-alkyl, alkyl, alkenyl, alkoxy, aryloxy, halogen, alkylthio,arylthio, carboxyalkyl, cyano, isocyanato, and the like, and employedasreactants in the novel process of this invention. Specific examples ofsuitable substituted-organic nitro compounds which can be used are asfollows:

. o-Nitrotoluene m-Nitrotoluene p-Nitrotoluene o-Nitro-p-xyleneZ-Methyl-l-nitronaphthalene m-Dinitrobenzene p-Dinitrobenzene2,4-Dinitrotoluene 2,6-Dinitrotoluene l0. Dinitromesitylene ll.4,4'-Dinitrobiphenyl l2. 2,4-Dinitrobiphenyl l3. 4,4'-Dinitrobibenzyll4. Bis(p-nitrophenyl)methane' l5. Bis(2,4-dinitrophenyl)methane 16.Bis(pnitrophenyl)ether I 17. Bis(2,4-dinitrophenyl)ether l8.Bis(p-nitrophenyl)thioether 19. Bis(p-nitrophenyl)sulfone 20.Bis(p-nitrophenoxy)ethane 21. a,a-Dinitro-p-xylene 22.2,4,6-Trinitrotoluene 23. 1,3,5-Trinitrobenzene 24.l-Chloro-Z-nitrobenzene 25. l-Chloro-4-nitrobenzene 26.l-Chloro-3-nitrobenzene 2-Chloro-6-nitrotoluene 4-Chloro-3-nitrotoluene1-Chloro-2,4-dinitrobenzene l,4-Dichloro-2-nitrobenzenealpha-Chloro-p-nitrotoluene l,3,5-Trichloro-2-nitrobenzenel,3,5-Trichloro-2,4-dinitrobenzene 1,2-Dichloro-4-nitrobenzenealpha-Chloro-m-nitrotoluene l,2,4-Trichloro-S-nitrobenzenel-Bromo-4-nitrobenzene l-Bromo-Z-nitrobenzene l-Bromo-3-nitrobenzene1-Bromo-2,4-dinitrobenzene a,a-Dibromo-p-nitrotoluene.d-Bromo-p-nitrotoluene I l'-Fluoro-4-nitrobenzene1-Fluoro-2,4-dinitrobenzene l-Fluord-Z-nitrobenzene .o-Nitrophenylisocyanate m-Nitrophenyl isocyanate p-Nitrophenyl isocyanateo-Nitroanisole .p-Nitroanisole p-Nitrophenetole o-Nitrophenetole2,4-Dinitrophenetole 2,4-Dinitroanisolel-Chloro-2,4-dimethoxy-S-nitrobenzene l ,4-Dimethoxy-2-nitrobenzenem-Nitrobenzaldehyde p-Nitrobenzaldehyde p-Nitrobenzoylchloridem-Nitroberizoylchloride 3,5-Dinitrobenzoylchloride Ethyl-p-nitrobenzoateMethyl-o-nitrobenzoate m-Nitrobenzenesulfonylchloridep-Nitrobenzenesulfonylchloride o-Nitrobenzenesulfonylchloride4-Chloro-3-nitrobenzenesulfonyichloride2,4-Dinitrobenzenesulfonylchloride 3-Nitrophthalic anhydridep-Nitrobenzonitrile m-Nitrobenzonitrile 1,4-DinitrocyclohexaneBis(p-nitrocyclohexyl)methane l-Nitro-n-hexane2,2-Dimethyl-l-nitrobutane 1,6-Dinitto-n-hexane l,4-Bis(nitromethyl)cyclohexane 78. 3,3'-Dirnethoxy-4,4-dinitro-biphenyl 79.3,3'-Dimethyl-4,4'-dinitro-biphenyl In addition, isomers and mixtures ofthe aforesaid organic nitro compounds and substituted organic nitrocompounds may also be employed, as well as homologues and other relatedcompounds. Compounds which have both nitro and isocyanato substituents,such as 2-isocyanato-4 nitrotoluene, may also be employed as a reactant.Aromatic nitro compounds are preferably employed as a reactant becausethe novel catalyst system of this invention appears to be more effectivefor these compoundsGenerally, the organic nitro compounds and substituedorganic nitro compounds contain between one and about 20 and preferablybetween about one and about 14 carbon atoms.

As indicated above, the catalyst system of this invention is a mixtureof at least one compound selected from the group consisting of palladiumhalides, rhodium halides, palladium oxides and rhodium oxides, with atleast one oxide of an element selected from the group consisting ofvanadium, molybdenum, tungsten, niobium, chromium and tantalum.Palladium halides include palladium bromide, palladium chloride,palladium fluoride, and palladium iodide. Rhodium halides includerhodium bromide, rhodium chloride, rhodium fluoride, and rhodium'iodide.Palladium oxides include palladium suboxide (Pd,0), palladium monoxide(PdO), and palladium dioxide (PdO,).

Rhodium oxides include rhodium monoxide (RhO),

rhodium sesquioxide (Rh,0,), and rhodium dioxide (RhO,). At least one ofthese halides or oxides or palladium or rhodium is used as a componentof the mixture used as the catalyst system, but mixtures of one or morehalides and one or more oxides may be employed as one component of thecatalyst mixture.

The other component of the catalyst mixture is at least one oxide of anelement selected from a group consisting of vanadium, molybdenum,tungsten, niobium, chromium, and tantalum. The elements are found inGroup VB and VlB of the Periodic Table. Suitable oxides of this typeinclude chromic oxide (C130,), chromium dioxide (CrO,), and chromousoxide (CrO);

molybdenum sesquioxide (M 0 molybdenum dioxide (MoO and molybdenumtrioxide (M00 niobium monoxide (NbO), niobium oxide (NbO and niobiumpentoxide (Nb O tantalum dioxide (Ta O tantalum tetraoxide (Ta O andtantalum pentoxide (Ta O tungstic oxide (W0 and tungstic trioxide (W0vanadium dioxide (V 0 vanadium trioxide (V 0 vanadium tetraoxide (V 0and vanadium pentoxide (V 0 Mixtures of two or more of these oxides maybe employed as one component of the catalyst mixture.

Although all of the foresaid catalyst systems have some effect uponincreasing the yield of organic isocyanates, certain systems aresignificantly more effective than others. Included in these moreeffective systems are the following:

1. Palladium chloride and vanadium pentoxide 2. Palladium chloride andmolybdenum dioxide 3. Rhodium trichloride and vanadium pentoxide 4.Rhodium trichloride and molybdenum dioxide 5. Palladium chloride,rhodium trichloride and vanadium pentoxide.

The catalyst system can be self-supported or deposited on a support orcarrier for dispersing the catalyst system to increase its effectivesurface. Alumina, silica, carbon, barium sulfate, calcium carbonate,asbestos, bentonite, diatomaceous earth, fullers earth, and analogousmaterials are useful as carriers for this purpose.

The reaction is carried out in the presence of a catalystic proportionof the catalyst system. The proportion of catalyst system is generallyequivalent to between about 0.1 and about 100 percent, and preferablybetween about 1 and about 60 percent by weight of the organic nitrocompound. However, greater or lesser proportions may be employed ifdesired.

The weight ratio of palladium or rhodium compound to oxide of the GroupVB or VIB metals in the catalyst system is generally in the rangebetween about 0.00111 and about 25:1, and preferably in the rangebetween about 0.05:1 and about 10:1.

The process of this invention operates effectively in the absence of asolvent, but improved overall yields of the organic isocyanates can beobtained when a solvent which is chemically inert to the components ofthe reaction system is employed. Suitable solvents include halogenatedaliphatic and aromatic hydrocarbons such as dichloromethane,tetrachloroethane, monochloronaphthalene, monochlorobenzene,

dichlorobenzene,a-chloronaphthalene, and perchloroethylene, as well assulfur dioxide, mixtures thereof and the like.

The proportion of solvent is not critical and any proportion may beemployed which will not require excessively large equipment to contain.Generally the weight percent of organic nitro compound in the solvent isin the range between about 5.0 and about 75 percent, but greater orlesser proportions may be employed if desired.

The order of mixing the reactants is not critical and may be variedwithin the limitations of the equipment employed. In one embodiment, theorganic nitro compound, catalyst system, and, if desired, solvent, ischarged to a suitable pressure vessel such as an autoclave which waspreviously purged with nitrogen, and which is preferably provided withagitation means such as a stirrer-tor an external rocking mechanism.Carbon monoxide is fed into the autoclave until a pressure is attainedwhich is in the range between about 30 and about 10,000 psig, andpreferably between about and about 8,000 psig, but greater or lesserpressures may be employed if desired.

Generally the quantity of carbon monoxide in the free space of thereactor is sufficient to maintain the desired pressure as well asprovide reactant for the process, as the reaction progresses. Ifdesired, additional carbon monoxide can be fed to the reactor eitherintermittently or continuously as the reaction progresses. The reactionis believed to progress in accordance with the following equation:

where R is the organic moiety of the organic nitro compound reactant ofthe type defined above, and n is the number of nitro groups in theorganic nitro compound. From Formula I, it can be seen that when R isaromatic, sufficient carbon monoxide is present to provide at least 3moles of carbon monoxide per mole of nitro groups reacted in saidaromatic nitro compound. The total amount of carbon monoxide addedduring the reaction is generally between about 3 and about 50, andpreferably between about 8 and about 15 moles of carbon monoxide. permole of nitro group in the organic nitro compound. Greater or lesseramounts may be employed if desired. The highest carbon monoxiderequirements are generally utilized in a process in which the carbonmonoxide is added continuously, but suitable recycle of the carbonmonoxide containing gas streams greatly reduces the overall consumptionof carbon monoxide.

The reaction temperature is maintained above about 25C and preferablybetween about 100 and about 250C. Interior and/or exterior heating andcooling means may be employed to maintain the temperature within thereactor within the desired range.

The reaction time is dependent upon the organic nitro compound beingreacted, and on the amount of catalyst being charged, as well as thetype of equipment being employed. Usually between one-half hour and 20hours are required to obtain the desired degree of reaction, but shorteror longer reaction times may be employed. v

The reaction can be carried out batchwise, semicontinuously orcontinuously.

After the reaction is completed, the temperature of the crude reactionmixture may be dropped to ambient temperature, the pressure vessel isvented, and the reaction products are removed from the reaction vessel.Filtration or other suitable solid-liquid separation technique may beemployed to separate the catalyst from the reaction product, thefractional distillation is preferably employed to isolate the organicisocyanate from the reaction product. However, other suitable separationtechniques such as extraction, sublimation, etc., may'be employed toseparate the organic isocyanate from the unreacted organic nitrocompound and any by-products that may be formed.

Organic isocyanates produced in accordance with the technique of thisinvention are suitable for use in preparing urethane compounds such asfoams, coatings, fibers, and the like by reacting the organic isocyanatewith a suitable polyether polyol in the presence of a catalyst and, ifdesired, a foaming agent, and as intermediates for biologically activecompounds.

The following examples are presented to further illustrate the inventionwithout any intention of being limited thereby. All parts andpercentages are by weight unless otherwise specified.

EXAMPLE 1 A rocking 316 stainless steel autoclave having a volume of 103ml. was charged with 6.0 g. (0.049 mole) of nitrobenzene in ml. ofchlorobenzene, 0.18 g. (1.0 X mole) of palladous chloride, and 0.36 g.(2.0 X 10' mole) of vanadium pentoxide. The reactor was closed, purged,and then pressurized with carbon monoxide to 1850 psi. The reactionmixture was heated to 190C and kept at this temperature for 1.5 hours.After cooling to room temperature, the autoclave was vented and thereaction mixture was filtered. A vapor phase chromatography analysis ofa portion of the weighed filtrate indicated that a corrected yield ofphenyl isocyanate of 56.0 percent, based on a nitrobenzene conversion of94.5 percent, was obtained.

EXAMPLE 2 A quantity of 6.0 g. (0.049 mole) of nitrobenzene in 5 ml. oforthodichlorobenzene was reacted with carbon monoxide at an initialpressure of 2180 psi. in the presence of 0.18 g. (8.6 X 10" mole) ofrhodium chloride and 0.12 g. (6.6 X 10- mole) of vanadium pentoxide for1.5 hours at 190C as described in Example 1. An analysis of the filtrateby vapor phase chromatography showed that the reaction afforded a 71.1percent corrected yield of phenylisocyanate, based on a 93.3 percentconversion of nitrobenzene.

EXAMPLE 3 A 103 ml. rocking autoclave filled with a glass insert wascharged with 6.0 g. (0.049 mole) of nitrobenzene, 0.12 g. (6.8 X 10*mole) of palladous chloride, and 0.12 g. (9.4 X 10" mole) of molybdenumdioxide. The reactor was closed, purged, and then pressurized withcarbon monoxide to 2,780 psi. The reaction mixture was heated to 190Cand kept at this temperature for 3.0 hours. An analysis of the filtrateas described in Example 1 showed that this system produced a 50.4percent corrected yield of phenyl isocyanate, based on a 95.3 percentconversion ofnitrobenzene.

EXAMPLE 4 A quantity of 6.0 g. (0.049 mole) of nitrobenzene was reactedwith carbon monoxide at an initial pressure of 4,990 psi. in thepresence of 0.18 g. (8.6 X 10 mole) of rhodium chloride and 0.18 g. (1.4X 10' mole) of molybdenum dioxide for 1.5 hours at 190C as described inExample 1. On the basis of vapor phase chromatography analysis thereaction afforded phenylisocyanate in a corrected yield of 50.7 percent,based on a 89.7 percent conversion of nitrobenzene.

EXAMPLE 5 An amount of 6.0 g. (0.049 mole) of nitrobenzene was reactedwith carbon monoxide at an initial pressure of 5,070 psi. in thepresence of 0.18 g. (1.3 X 10 moles) of palladium dioxide and 0.18 g.(1.0 X 10' mole) of vanadium pentoxide for 1.5 hours at 190C asdescribed in Example 1. A vapor phase chromatography analysis of thefiltrate indicated that the reaction produced a 69.5 percent correctedyield of phenyl isocyanate, based on a nitrobenzene conversion of 32.3percent.

EXAMPLE 6 Nitrobenzene (0.05 mole) was added to the autoclave of Example3 along with 3 percent rhodium trichloride, 3 percent vanadium pentoxideand 3 percent molybdenum dioxide. The pressure ranged from 1,925 to2,875 psi. over the 1.5 hour reaction period, and the temperature was190C. The reaction produced a corrected yield of 51 percent phenylisocyanate based on a nitrobenzene conversion of percent.

For purposes of comparison the above procedure was repeated except thatthe catalyst system was a mixture of 3 percent palladous chloride and 3percent rhodium trichloride, and the reaction was carried in 5milliliters of orthodichlorobenzene solvent. The reaction resulted inthe conversion of 17 percent of the nitrobenzene to unknown compounds,with no detectable amount of isocyanate being formed. I

EXAMPLES 7-18 The procedure of Example 1 was repeated, utilizingnitrobenzene (0.05 moles) as the starting material. In each example, thereaction temperature was 190C and the reaction time was minutes. Theproportions, catalyst, pressure range, are set forth below in the table.The table also shows the percent conversion-and the percent correctedyield of phenyl isocyanate.

Pressure Conver- Example Catalyst, Catalyst, Catalyst, range, slon,Yield, No. percent percent percent p.s.i.g. percent percent .0 M001, 6.0Tarot, 1.0 1, 475-2165 32 39 .0 V105, 6.0 Tazoi, 1.0 1, 185-2, 45 36 17-RhCl ,3.0 V20 2.0 u 2, zoo-3,220 75 43 1s PdClz, 1.0 V20 6.0 1, 236-1,800 38 4 I Reaction carried out in ortho-dichlorobenzene solvent. bBased on V205 content of aluminum silicate impregnated with 5% V105.Based on V20 content of silica impregnated with 10% V105.

EXAMPLE 19 A 300 milliliter stainless steel autoclave provided with amechanically driven agitator, internal cooling coil, an external heatingmantle, and a gas sparger for feeding carbon monoxide into the bottom ofthe autoclave was employed in this example. Dinitrotoluene (50 grams),monochlorobenzene (50 grams), palladium chloride (3 grams) and vanadiumpentoxide (2 grams) were charged to the autoclave. The autoclave andauxiliary equipment were assembled, the agitator was started, and heatwas applied to raise the internal temperature within the range between160 and 170C. Carbon monoxide was fed through the sparger at a ratebetween 500 and 1,000 cc per minute, while maintaining a carbon monoxidepressure of about 500 psig. After 4 hours and 20 minutes, the flow ofcarbon monoxide was stopped, the reaction mixture was cooled by passingcooling water through the internal coils, and the pressure was releasedfrom the vessel. Analysis of the reaction product showed a conversion of29.6 percent, and a corrected yield of 0.73 percent toluenediisocyanate, 2.9 percent of 2-nitro,4-isocyanato toluene, and 68.8percent 4-nitro,2-isocyanato toluene.

EXAMPLE 20 The procedure of Example 19 was repeated with the followingexceptions. The charge to the autoclave was dinitrotoluene (50 grams),orthodichlorobenzene (120 grams), palladium chloride (5 grams), rhodiumtrichloride (5 grams), and vanadium pentoxide grams). The reaction wascarried out at a temperature of 184C and a pressure of 1000 psig, with afeed rate of carbon monoxide of 1,000 cc per minute. The reaction timewas 8 hours and 45 minutes. Analysis of the reaction product showed aconversion of 94.5 percent, with a corrected yield of toluenediisocyanate of 42.9 percent, of 2-nitro,4-isocyanato toluene of 10.7percent, and of 4-nitro,2-isocyanato toluene of 47.6 percent.

EXAMPLE 21 The procedure of Example 1 was repeated, employing thefollowing ingredients in the following proportions:

ingredients Proportions Dinitrotoluene 0.05 moles Rhodium Trichloride 4percent Palladium Chloride 2 percent Vanadium Pentoxide 2 percentMonochlorobenzene 5 milliliters EXAMPLE 22 A 300 milliliter stainlesssteel autoclave provided with a mechanically driven agitator, internalcooling coils, and an external heating mantle was employed inCOMPARATIVE EXAMPLES A-F The procedure of Examples 7-18 was repeatedwith the exception that the catalyst system employed was comprised of anoble metal compound and a Lewis acid. The proportions, catalyst,pressure range, percent conversion and percent corrected yield of phenylisocyanate are set forth below in the table.

EX. Catalyst ield,

Catalyst Pressure Conver- Y range sion psig A PdO,,1 SbC1 ,6 1450-2080ND 0 B PdCl J SbC1 ,6 1490-2100 ND 0 C RhCl,,1 SbCl ,6 1350-1920 ND 0 DPdCl,,1 SbF,,6 1400-2000 ND 0 E PdCl,,l AsCl;,,6 1190-1700 ND 0 FRhC1,,1 AsCl,,6 1270-1800 6.5 8

ND-Not Detennined These comparative Examples demonstrate that when Lewisacids such as antimony trichloride, antimony trifloride and arsenouschloride are used in combination with noble metal compounds as acatalyst system in the reaction of nitrobenzene with carbon monoxide,there is little or no formation of phenyl isocyanate.

EXAMPLE 23 The apparatus of Example 19 was employed in this Example. Thecharge to the autoclave was 129 grams of orthodichlorobenzene, 50 gramsof dinitrotoluene parts of 2,4-and 20 parts of 2,6-dinitrotoluene), anda mixture of 5 grams rhodium trichloride, 5 grams palladium dichlorideand 15 grams of vanadium pentoxide, the mixture being ground to form afine powder. The reaction was carried out for 6 hours, during which timethe temperature ranged from 188 to 192C, the pressure was approximately1,000 psig and the feed rate of carbon monoxide was between 1,000 and1,500 cc per minute. Analysis of the product showed that there was aconversion of 89 percent of the dinitrotoluene, and a corrected yield of41.0 percent toluene diisocyanate (a mixture of the 2,4- and 2,6-isomers), 26.5 percent of 2-nitro-4-isocyanato toluene, and 25.7 percentof 4-nitro-2-isocyanato toluene.

What is desired to be secured by Letters Patent is:

l. A process for preparing an aromatic isocyanate which comprisesreacting at an elevated temperature and an elevated pressure, anaromatic nitro compound containing up to 20 carbon atoms with carbonmonoxide in the presence of a catalyst system, Which comprises employingas said catalyst system a mixture of a. a compound selected from thegroup consisting of palladium halides, rhodium halides, palladiumoxides, and rhodium oxides, and

b. an oxide of an element selected from the group consisting ofvanadium, molybdenum, tungsten, niobium, chromium and tantalum,

. wherein the proportion of said catalyst system is between about 0.1and about 100 percent by weight of said aromatic nitro compound, and

. wherein sufficient carbon monoxide is present to provide at leastthree moles of carbon monoxide per mole of nitro groups reacted in saidaromatic nitro compound.

2. The process of claim 1 wherein the weight ratio of said compound (a)to said oxide (b) is in the range between about :05z1 and :1.

3. The process of claim 2 wherein said elevated pres sure is in therange between about 100 and 8,000 psig.

4. The process of claim 2 wherein said process is carried out in thepresence of an inert solvent selected from the group consisting ofhalogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons,and mixtures thereof.

5. The process of claim 2 wherein said elevated temperature is in therange between about 100 and 250C.

6. The process of. claim 2 wherein said aromatic nitro compound isnitrobenzene, dinitrotoluene or isocyanato nitrotoluene.

7. The process of claim 6 wherein said catalyst system is a mixture ofpalladium chloride and vanadium pentoxide.

8. The process of claim 6-wherein said catalyst system is a mixture ofpalladium chloride and molybdenum oxide.

9. The process of claim 6 wherein said catalyst system is a mixture ofrhodium trichloride and vanadium pentoxide.

10. The process of claim 6 wherein said catalyst system is a mixture ofrhodium trichloride and molybdenum oxide.

11. The process of claim 6 wherein said catalyst system is a mixture ofrhodium trichloride, palladium chloride and vanadium pentoxide.

12. A process for preparing aromatic isocyanates which comprisesreacting an aromatic nitro compound with carbon monoxide in the presenceof a catalyst mixture of palladiumhalides, rhodium halides, palladiumoxides or rhodium oxides, and an oxide of molybdenum. I

1. A process for preparing an aromatic isocyanate which comprisesreacting at an elevated temperature and an elevated pressure, anaromatic nitro compound containing up to 20 carbon atoms with carbonmonoxide in the presence of a catalyst system, Which comprises employingas said catalyst system a mixture of a. a compound selected from thegroup consisting of palladium halides, rhodium halides, palladiumoxides, and rhodium oxides, and b. an oxide of an element selected fromthe group consisting of vanadium, molybdenum, tungsten, niobium,chromium and tantalum, c. wherein the proportion of said catalyst systemis between about 0.1 and about 100 percent by weight of said aromaticnitro compound, and d. wherein sufficient carbon monoxide is present toprovide at least three moles of carbon monoxide per mole of nitro groupsreacted in said aromatic nitro compound.
 2. The process of claim 1wherein the weight ratio of said compoUnd (a) to said oxide (b) is inthe range between about 0: 05:1 and 10:1.
 3. The process of claim 2wherein said elevated pressure is in the range between about 100 and8,000 psig.
 4. The process of claim 2 wherein said process is carriedout in the presence of an inert solvent selected from the groupconsisting of halogenated aliphatic hydrocarbons, halogenated aromatichydrocarbons, and mixtures thereof.
 5. The process of claim 2 whereinsaid elevated temperature is in the range between about 100* and 250* C.6. The process of claim 2 wherein said aromatic nitro compound isnitrobenzene, dinitrotoluene or isocyanato nitrotoluene.
 7. The processof claim 6 wherein said catalyst system is a mixture of palladiumchloride and vanadium pentoxide.
 8. The process of claim 6 wherein saidcatalyst system is a mixture of palladium chloride and molybdenum oxide.9. The process of claim 6 wherein said catalyst system is a mixture ofrhodium trichloride and vanadium pentoxide.
 10. The process of claim 6wherein said catalyst system is a mixture of rhodium trichloride andmolybdenum oxide.
 11. The process of claim 6 wherein said catalystsystem is a mixture of rhodium trichloride, palladium chloride andvanadium pentoxide.